1. Field of the Invention
The present invention relates to a structure for tightly closing a light exit end of a rod integrator disposed on an optical path in order to homogenize the luminous flux density within a plane perpendicular to the optical axis in an illumination optical system of a projection type image display apparatus or the like, and a rod integrator holder.
2. Description of the Prior Art
In illumination optical systems of projection type image display apparatus such as video projectors in which illumination light is optically modulated by an image display device such as digital micromirror device (hereinafter referred to as “DMD”) and thus modulated light is projected under magnification, optical prisms known as rod integrators have conventionally been used as means for homogenizing the luminous flux density in order to illuminate the image display device uniformly. The rod integrators have been configured such that an incident luminous flux is repeatedly totally reflected therewithin and then is emitted therefrom while the luminous flux density distribution within a plane perpendicular to the optical axis becomes substantially uniform. In particular, within an illumination optical system, a rod integrator is often disposed downstream a color wheel apparatus acting as color decomposing means.
As a holding structure for holding this kind of rod integrator within an illumination optical system, the type disclosed in Japanese Unexamined Patent Publication No. 8-227034, for example, has been known in general. This type of rod integrator holding structure is configured such that a rod integrator inserted in a hollow rod integrator holder made of die-cast aluminum or the like having a side face formed with an opening is supported at both ends of the rod integrator holder, and a side face of the rod integrator is pressed with a leaf spring attached to the opening so as to be secured to the rod integrator holder.
Meanwhile, heat sources such as a light source are disposed within a housing of a projection image display apparatus such as video projector in which a rod integrator is placed, and the housing is provided with intake and exhaust fans for letting out the heat emitted from the heat sources. Also, the apparatus housing is formed with an opening in the vicinity of each fan when appropriate so as to allow the air to communicate between the inside and outside thereof, through which dust, smoke, and the like may flow in.
In general, an illumination optical system using a rod integrator is configured such that the light exit face of the rod integrator and the device surface of an image display device have an optically conjugate relationship therebetween. Therefore, if the light exit face of the rod integrator is damaged or dust or the like attaches thereto, an image of dust or the like will be formed on the device surface of the image display device. The image of damage, dust, or the like formed on the device surface is superposed on an image displayed by the image display device, and is projected onto a screen under magnification.
It has been difficult for the above-mentioned conventional rod integrator support structure to prevent the dust, smoke, or the like having flown into the apparatus housing from attaching to the light exit face of the rod integrator and keep the light exit face from being damaged. As a consequence, there has been a fear of the image quality deteriorating on the screen when a rod integrator having such a support structure is used.
Also, the conventional rod integrator holder configured as mentioned above has failed to provide means for preventing the dust, smoke, and the like having flown into the apparatus housing from attaching to the light exit face of the rod integrator or keep the light exit face from being damaged. Therefore, it has been difficult for such a rod integrator holder to prevent dust or the like from attaching to the light exit face or keep the light exit face from being damaged, thus yielding a fear of the image quality deteriorating on the screen.